The present invention relates generally to charging devices for use in electrostatographic devices and more particularly to corona-charging devices for use in such machines, which provide repairable and replaceable structures.
Generally, the process of electrostatographic copying is executed by exposing a light image of an original document to a substantially uniformly charged photoreceptor member. Exposing the charged photoreceptor member to a light image selectively discharges the photoconductive surface thereof to create an electrostatic latent image of the original document on the photoreceptor member. The electrostatic latent image is subsequently developed into a visible image by a process in which charged developing material is deposited onto the photoconductive surface of the photoreceptor such that the developing material is selectively attracted to the image areas thereon. The developing material is then transferred from the photoreceptor member to a copy sheet on which the toner image may be permanently affixed to provide a reproduction of the original document. In a final step, the photoconductive surface of the photoreceptor member is cleaned to remove any residual developing material therefrom in preparation for successive imaging cycles.
The described process is well known and is useful for light lens copying from the original as well as the printing of documents from electronically generated or stored originals. Analogous processes also exist in other electrostatographic applications such as, for example, digital printing applications where latent images are generated by a modulated laser beam or LED printhead, or ionographic printing and reproduction processes in which charges are selectively deposited on a charge retentive surface in accordance with an image stored in electronic form.
In electrostatographic applications, it is common practice to use corona-generating devices for providing electrostatic fields to drive various machine operations. Such corona devices are primarily used to deposit charge on the photoreceptor member prior to exposure to the light image for subsequently enabling toner transfer thereto. In addition, corona devices are used in the transfer of an electrostatic toner image from a photoreceptor to a transfer substrate, in tacking and detacking paper to or from the imaging member by applying a neutralizing charge to the paper, and, generally in conditioning the imaging surface prior to, during and after toner is deposited thereon to improve the quality of the xerographic output copy.
In use, corona-generating wires are noted for the ability to produce reasonably uniform charge on a surface to be charged. However, over time, the environment to which the corona generating wire is exposed begins to cause irregularities and degradation in charging uniformity. These irregularities may be traced to surface irregularities on the coronode""s surface, which over time becomes pitted, or coated with toner or fuser release agent or other process by-products which must be removed. While cleaning the wire serves to improve the charging characteristics, the wires eventually require replacement due to further degradation in performance or breakage, which often occurs while cleaning.
The problem of stringing the corona generating wires into position has been long recognized and various approaches have been suggested in the prior art. The primary difficulty in the procedure is to obtain the appropriate tension on the wire but yet provide for some ease in replacement of the wire. If the tension is too low an undesirable sinking of the wire occurs, with resultant charging nonuniformity. If the tension is too high, breakage of the wire may result. It would be highly desirable to have a corona-charging device that allows for stringing of a corona generating wire in a relatively simple manner so that a moderately trained user, rather than a service representative, may change or replace the corona generating wire with relative ease. Alternatively ease of replacement advantageously decreases the time a service representative is required to perform this task during a service call.
These and other objects of the invention, which will become more apparent after reading of the specification, are realized by:
In accordance with one aspect of the invention there is provided a support and tensioning device for an elongated corona generating electrode comprising a corona charger shield member that is longitudinally extending in a longitudinal direction and includes a first set of wall members for serving as a shield for a corona generating electrode and the shield member including a longitudinally extending opening through which corona charge emanating from a corona electrode may flow to a surface to be charged, the shield member including a second set of wall members shaped to define a recess formed at one end of the shield member for receiving therein a plunger member and a spring, the recess including an inner positioned land for engaging a head end of the spring, and the second set of wall members defining the recess including walls located to define a key slot opening which extends in the longitudinal direction of the shield member; a spring residing in the recess and the head end of the spring engaging the land to restrict movement of the head end of the spring within the recess, the spring also having a tail end; a hollow plunger member having a generally cylindrical sidewall for supporting the plunger for rotational movement in the recess and a land on or near a head end portion of the plunger member engaging the tail end of the spring, the plunger member including a wall having a slug receiving opening for receiving a slug formed on one end of the corona electrode and a slot extending from the slug receiving opening in the wall towards the head end portion of the plunger member, a key extending radially from the generally cylindrical sidewall and located within the key slot opening for sliding movement therein to permit tensioning of the corona electrode, the recess receiving the plunger member to permit rotation of the plunger member about the axis of rotation of the generally cylindrical wall to locate the key in the key slot opening to lock the plunger member into the corona charger shield member.
In accordance with a second aspect of the invention there is provided a method of supporting and tensioning an elongated corona generating electrode comprising providing a corona charger shield member that is longitudinally extending in a direction and includes a first set of wall members for serving as a shield for a corona generating electrode, the shield member including a longitudinally extending opening through which corona charge emanating from a corona generating electrode may flow to a surface to be charged, the shield member including a second set of wall members shaped to define a recess formed at one end of the shield member for receiving a hollow plunger member and a spring, the recess including an inner positioned land for engaging a head end of the spring, and the second set of wall members defining the recess including a key slot opening which extends in a longitudinal direction of the shield member; placing a spring so as to reside in the recess with the head end of the spring engaging the land to restrict movement of the head end of the spring within the recess, the spring also having a tail end; advancing a hollow plunger member into the recess, the plunger member having a key that is moved within an entry slot formed proximate the one end of the shield member, the advancement of the plunger member being against a bias force of the spring; pivoting the plunger member to seat the key against a keeper wall defining one end terminus of the key slot formed in the one end of the shield member within which the key is free to move; placing a slug within a slug receiving opening formed in the plunger member, the slug being attached to one end of the corona generating electrode; restraining a second end of the corona generating electrode with a keeper located proximate a second end of the shield member; and the key being free to move within the key slot to establish a tension in the electrode under spring bias imposed by the spring.